LONDON — Six days and 3,300 miles from the bombings in Boston, the London Marathon was held Sunday under an azure sky, in what runners called perfect conditions, with no security scares and the minds of virtually all involved soaring westward to the victims of last Monday’s attack.

No world records fell on a brisk but practically windless day, and the main events, the men’s and women’s races, were won by competitors who were among the favorites among the roughly 35,000 competitors. The men’s race was won by the Ethiopian Tsegaye Kebede, a previous winner, in 2 hours 6 minutes 4 seconds, and the women’s race by the Kenyan Priscah Jeptoo, in 2:20.15, both well outside the world records.

The women’s wheelchair race was won by the 24-year-old Russian-born American Tatyana McFadden, who won the same event in Boston last Monday.

She was one of fewer than 20 competitors who took part in both marathons, according to the London organizers, and she came to London saying she planned to carry the memory of those killed and injured with her in the race. “Today was about running for Boston,” she said at the finish.

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Tsegaye Kebede of Ethiopia was the men's winner of the London Marathon on Sunday.CreditAlastair Grant/Associated Press

Organizers hailed the event, the 33rd annual running of a classic that passes the Houses of Parliament and ends on the Mall, the great avenue overlooked by Buckingham Palace, as the most successful in its history. It was also probably the most emotional, for all it said about the ties that bind marathoners worldwide and the depth of history and sentiment that links Britain and the United States.

More than anything, there was relief that concerns about a possible copycat attack modeled on the bombings that killed three people and injured more than 170 at the finish of the Boston Marathon proved groundless. Apart from a few routine medical emergencies along the course, the only jarring incident involved an on-course collision at a refreshment station that put one of the top-ranked competitors in the women’s race, the 2012 Olympic champion Tiki Gelana of Ethiopia, out of contention, and a front-runner in the men’s wheelchair division, Josh Cassidy of Canada, out of the race.

But there was far more to the event’s success, as reflected in a mood that mixed celebration, commemoration and defiance among runners, organizers and a crowd along the 26.2-mile route that the police estimated included at least a half-million people. Veteran competitors said the throngs along the way appeared to be the largest since the event was established in 1981 by founders who used the Boston event, first run in 1897, as their template.

There was an array of American flags among spectators, waved by children on their fathers’ backs and tied to the security barriers lining the course, which begins in the leafy southeast London suburb of Blackheath. It winds along both sides of the Thames, past the Tower of London and through London’s financial district, before a closing stretch from Parliament to the packed spectator areas near the palace.

One big red banner hoisted by spectators near the start read simply, “For Boston.” Many of the runners wore black ribbons provided by organizers on their vests, in commemoration of the Boston casualties. Organizers pledged before the race to donate about $3 for every competitor who finished the race to the One Fund Boston campaign, established by Gov. Deval Patrick of Massachusetts and Mayor Thomas Menino of Boston to help those most affected.

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Priscah Jeptoo of Kenya won the women's race.CreditAlastair Grant/Associated Press

Before the start, a single whistle blow summoned a sea of runners stretching shoulder to shoulder for a thousand yards to observe 30 seconds of silence. The official commentator for the event, Geoff Wightman, addressed the competitors and set the mood.

“Marathon running is a global sport,” Wightman said. “It unites runners and supporters on every continent in pursuit of a common challenge and in the spirit of friendship and fellowship. This week, the world marathon family was shocked and saddened by the events in the Boston Marathon.

“In a few moments, a whistle will sound, and we will join together in silence to remember our friends and colleagues for whom a day of joy turned into a day of sadness. Let us now show our respect and support for the victims of the Boston tragedy.”

Television images from an overhead blimp showed the mass of runners falling still, some with hands clasped in prayer, some gazing to the sky, others with eyes downcast.

Like many of the world’s major marathons, the London race has traditionally drawn the world’s fastest runners but has filled out the field with thousands of amateurs, many of them raising money for charities, and, in London particularly, with lighthearted competitors who turn out in an array of fancy dress. Apart from the wheelchair races, which attract paralympic champions, there are hundreds of disabled competitors, some of them legally blind, some of them war amputees.

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London Marathon runners observed a moment of silence on Sunday to honor the victims of the Boston Marathon bombings.

This year, the field included individuals dressed as a city slicker in a pinstripe suit, a Roman centurion, a Mr. Fix-It with a ladder, a baby, a schoolboy in short pants, a gas cooker, a soccer trophy and a variety of animals: a tiger, a gorilla and a rhinoceros. Scores of celebrities participated, from rock stars to actors, broadcasters to politicians. Some competitors who are freighted with heavy equipment, like the gas cooker, or with particularly severe disabilities, can take days to complete the course.

The money raised for charity is serious business — a total that has reached close to $1 billion over the three decades the race has been run, according to organizers’ records. No other sports event in Britain comes close, and the mood, at what has become a rite of spring, is serious for athletes and others testing their physical endurance, and jovial for others. This year, the joviality was as evident as ever, but so, too, was the sense of resolve that the Boston victims be honored appropriately.

Among those who commemorated the Boston victims was Prince Harry, the 28-year-old third-in-line to the British throne, who handed out medals to the winners and mingled with the crowds along the Mall, the ceremonial avenue that runs to Buckingham Palace, home to his grandmother Queen Elizabeth II.

An army attack helicopter pilot recently returned from a combat tour in Afghanistan, Prince Harry lingered near the finish line until the moment that some thought was potentially the most hazardous — four hours after the start, the time chosen by the Boston attackers, and one in which the crowd of runners reaching the marathon’s end are at their thickest.

Prince Harry’s memories of the Mall go back to the funeral of his mother, Princess Diana, when as a youth he walked behind her horse-drawn coffin as it rolled down the broad avenue. He told reporters he had never thought about canceling his appearance, any more, he said, than the marathon organizers had considered canceling the race.

“It’s fantastic, typically British,” he said.

“People are saying they haven’t seen crowds like this along the route for eight years,” he added, referring to the interval since the 2005 terrorist bombings that claimed 52 victims on London’s transit system, which spread public alarm about the safety of events like the marathon. “It’s remarkable to see.”

Correction:April 21, 2013

An earlier version of this article misstated where the London Marathon ends. It ends on the Mall, not on Pall Mall.

A version of this article appears in print on , Section D, Page 1 of the New York edition with the headline: Festive and Defiant, London Runs a Marathon for Boston. Order Reprints | Today’s Paper | Subscribe